Telephone-transmitter.



L, (i H. L. BRADLEY. TELEPHONE TRANSMITTER. APPLICATION FILED DEC. 26 LEG'ZQZ55B ,1908- RENEWED JAN.19,1914.

Patented Aug. 18, 129% Minesses.

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1 HARRY L. Blnmnnr, citizens of 1,107,255. Application filed December 2c, 1908, Serial No. 469,395.

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j "LYD-I'DE' BRADLEY AND HARRY L. BRADLEY,

" ALLEN-BRADLEY COMPANY, AoonPoRATIoN or WISCONSDL, v

' trnLnrnonn-trimusrrrrrnn- Tooll 107mm it miz-li concern Be it known that-we, Lrnnn BRADLEY and i the United States of America, and residents of Muskegcn, county of Muskegon, and State of Michigan, haveinvented a new and useful Improvement in 'Telephone-Transmitters, of.

which the following is a specification.

Our invention pertains to telephonetransmitters and particularly to the resistor thereof, vi'z., to the resistance medium forming a part of the transmitter and serving to {any the resistance of the electrical path through the transmitter in response to the movement of the transmitter diaphragm.

It relates particularly to variable resistances comprising contact elements which vary the resistance of the electrical path in response to changes of pressure.

The mechanism for compressing and re'- lieving the pressure on the resistor forms no part of the present invention, a typical de vice being shown.

Our invention provides av new resistance element for telephone transmitters of the granular carbon type of construction, our improved substance being utilized for the granular or comminuted material and for the disks or contact-faces as well.

Our invention comprisesthe production of resistance elements which comprise bodies of high conductivity internally and with high contact resistance as a surfacing thereupon. Specificallyive prefer to produce a body of carbon in its form of graphite surfaced with carbon in its amorphous form. t

In the drawings, Figure 1 shows a complete telephone transmitter; Fig. 2 shows on an enlarged scale the variable resistance parts thereof; Fig. 3 and Fig. 4 show the.

contact plates or'disks, and 5 shows .an'; alternative form of comminuted material. In the transmitter, which is typlcal of all the besttypcs of granular carbon "transmitters, carbon disks 1 and 2 are soldered or otherwise aflixcd to metal holders.

3 andl and comminuted material 5 is placed in the space between these.

In the preferred iorm of our invent on,

the disks 1 and 2 are of graphite treated to produce a surface of amorphous carbon. The process whereby we attainthis result is as follows: 'I.he, disks or plates are cut or sawed from rodsof artificial graphite so Specification of Letters Patent.

or MUSKEGON, .1VIICHIGAN, assreuons To Patented Au 18, 1914'. Renewed Januar 19, 1914'. Serial No. 813,113.

that the flat faces are parallel. The plates then are placed in a tray and properly su ported so that the flat faces will'not ma re contact with each other.' This is done in order that the flatfaces all may have free,

' I full and equal access to the solution 1n which they are to be placed. Then they are immersed. in a'tank containing coal tar thinned by a light oil of the same nature as the tar. The refined coal tar andlight oil which we use are obtained as follows: In the processes of making gas from coal, there is produced a crude coal tar which, when refined, yields refined coal tar, light oil and other substances. 1t is "the refined coal tar and light oil thus obtained that we use as a bath in preparing ourim'proved resistance element and our improved resister. The consistency of the tar and oil bath may be varied as desired. The heavier the bath used, the higher will be the resistance of the resulting resistor. During the first few minutes of immersion-the thinning oil enters the plates and leaves a coating of thick tar remaining on the surface, but by the end of about fifteenminutes this sticky coat has been dissolved. After immersion for a suflicie'nt length of time, the disks and the tar mixture are placed in a centrifugal 'separator'and, if necessary, more of the tar mixture is added'to insure com plete immersion of the dlsks 1n the separa'- tor. The'surplus tar mixture is thrown from the disks centrifugally The disksthen are brushed .to remove still further the adhering tar mixture. They are then placed in an oven andrkeptat-(ifi degrees C.-

for about twenty-four hours and again are brushed. This gives themav pollsh and a smooth surface and-tends to prevent sticking together (hiring-further'baking. They are thenpacked in tin tubes, placed. in an oven and baked at constantly .ii'lcreasing' temperaturcs, ten hours at 100 degrees (3., ten hours at 150- degres O, ten hours at QOOdegrees C., ten hours at 800 degrees C. They are then allowed to cool and are placed in a cast iron retort and are raised to 800 disk slightly, thus removing a portion of the high resistance coating which the disk acquires by its tar treatment. If the re sistance of any disk is not high enough the disk may be subjected to the treatment repeatedly. The disk thus treated may be copper plated upon one of its faces, whereby it may be soldered to its metallic support, tier 4.

The ability aiiorded by. the foregoing,

process of producing disks or plates of var ant 'resistanees'is advantageous, both in the matter of manufacture of the disks and of the comminuted material to be placed between the disks, since it permits the manufeature of transmitter resistance cells whose limiting resistances may be comparatively high or comparatively 'low. Adopting a musical analogy, the range of the resistor thus may be placed in any selected register. The. production of'transmitter resistors of .high or low limiting resistances is very important in telephone work. Local battery transmitters for local work operate most satisfactorily with a low resistance; central energy transmitters requiring a higher limiti resistance for local work, and transmitters of both classes operating to better advantage for long distance transmission when built with still higher limiting resistances.

In preparing the comminuted material, the process is substantially the same as for the disks except that the granules or spherules are kept constantly agitated to secure as far as possible an even treatment of'their surfaces.

In'Fig. a form of comminuted material is shown at 6, which" comprises broken sheet material. In the preparation of this material, plates of any convenient size, say an inch in diameter and as thin can be handled conveniently, say 1/100, are treated on both sides according to'the process above described, aiid then are broken and the fragments sifted through screens to grade them to desired limitations of size. The result is the comminuted material of Fig. 5 which is of value as a resistor, for variable resistance It is particularly important in this classof instruments that the material shall retain these properties permanently so as to pre vent the deterioration of the transmitter, and the treated graphite of our invention has proven in experiment and'in practice to have such properties.

While we have outlined in this specification with considerable detail the process of manufacture which we have found to be successful, we do not wish to be limited in our claims to the exact details specified, as

it is obvious that changes might be madewithin the skill of one versed in the arts without departing from the spirit of our invention.

Having thus described our invention, What we claim as new and desire to secure by United States Letters Patent is:

1. As a transmitter resistor, two graphite plates surfaced with amorphous carbon and comminuted material tlierebetween.

2. As a transmitter resistor, two graphite plates surfaced with amorphous carbon and graphite granules therebetween, said granules also being surfaced with amorphous carbon.

3. In a transmitter resistor, a plate of carbonaceous material of high conductivity surfaced with a coating of conducting amorphous carbon, substantially as described.

4. A variable resistor comprising two 0p--.

positely placed plates of low resistance carbon surfaced with' comparati ely .high resistance amorphous carbon. 7 5. In a telephone transmitter, a compressible variable resistor containing a comminuted material, each element. of which comprises a graphite body having a surface of carbonized coal tar.

(3. In a telephone transmitter,;a compressible variable resistor containing acomiiiiiiuted material, each element of which coiiipi'ises a conducting body having a car-- bonized coal tar surface thereon.

I. In a telephone transmitter, a compressible V variable resistor consisting of two plates of carbonaceous material and comminutcd carbonaceous material therebetween,

said plates and said coinininuted material each consisting of a body of high conductivity surfaced by a coating of carbonized coal tar.

Signed by us at Muskegon, county of Muskeg-on and State of Michigan, in the presence of two witnesses,

LYNDE BRADLEY. HARRY L, BRADLEY.

Witnesses;

JOHN VANnERwnuP, Josin' VANDERWERR. 

